Field of the Invention
The invention relates to a circuit configuration for supplying a telephone subscriber loop with a supply voltage, for transmitting a transmitted signal into the telephone subscriber loop, and for receiving a received signal from the telephone subscriber loop. The invention also relates to a network-side terminal of a telephone subscriber loop having the circuit configuration. The invention furthermore relates to a chip set for supplying a telephone subscriber loop with a supply voltage, for transmitting a transmitted signal into the telephone subscriber loop and for receiving a received signal from the telephone subscriber loop.
A known configuration with which it is possible to supply an ISDN subscriber loop by wiring a semiconductor component, is described below and illustrated in FIG. 3.
A circuit configuration for supplying a subscriber line is known from European Patent Application 0 663 755 A1. That circuit configuration is suitable in a particularly beneficial way for conventional analog subscriber lines. A transfer of that supply concept to ISDN subscriber lines presents problems because of unacceptable power losses generated by that circuit configuration, which does not include a transformer. In the case of an analog subscriber line, an operating time of 1% is assumed, during which it is necessary to supply the subscriber line. In contrast, an operating time of 40% is assumed for ISDN subscriber lines, during which a complete supply of the subscriber line is necessary. In the case of an ISDN telephone subscriber line the supply voltage must also be applied outside the operating time in order to supply the subscriber""s network terminal NT with energy in the quiescent mode. Due to analog technology that is used, a fluctuating supply voltage on an analog subscriber line is not critical for the functioning of the total system. However, in the case of an ISDN subscriber line, the connection is broken if the supply to the subscriber""s network terminal NT falls below a minimum value. The circuit configuration in European Patent Application 0 663 755 is not suitable for use at an ISDN subscriber line because of a high power loss.
It is accordingly an object of the invention to provide a circuit configuration and a chip set for supplying a telephone subscriber loop with a supply voltage and a network-side terminal of a telephone subscriber loop, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which require as few complex discrete components as possible and thereby guarantee a low power loss.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration for supplying a telephone subscriber loop having first and second lines or ends with a supply voltage, for transmitting a transmitted signal into the telephone subscriber loop, and for receiving a received signal from the telephone subscriber loop, the circuit configuration comprising a power supply voltage source having a first terminal and a second terminal across which a supply voltage drops or is applied; a first circuit connected to the first line, the first circuit having first and second supply voltage connections; and a second circuit connected to the second line, the second circuit having third and fourth supply voltage connections; the first supply voltage connection connected to the first terminal of the supply voltage source and the fourth supply voltage connection connected to the second terminal of the supply voltage source.
The advantage of this circuit configuration is that through an appropriate choice of the supply voltage and of the supply voltages of the first and second circuit, on one hand a pre-defined battery voltage can be guaranteed between the ends of the telephone subscriber loop, and on the other hand a wanted or desired signal of the subscriber loop can be applied over the first and second circuits in the range of their supply voltages and can be injected from the subscriber loop. The circuit does not require a transformer for this purpose. The power loss in the first and second circuits is reduced to a minimum because voltage drops generating losses are not oriented on the level of the supply voltage source but rather on the level of the supply voltages of the first and second circuits.
In accordance with another feature of the invention, the voltage between the first and the second supply voltage connections and the voltage between the third and the fourth supply voltage connections of the respective first and second circuits are chosen to be substantially lower than the voltage of the supply voltage. The choice of an especially small supply voltage for the first and second circuits can reduce the power loss of the circuit configuration to a minimum.
In accordance with a further feature of the invention, the first and second circuits each have an output driver circuit which is connected with the respective first and second ends of the subscriber loop. In this way it is possible to apply a wanted signal to the subscriber loop.
In accordance with an added feature of the invention, the first and second circuits also each have a current measuring device which measures the current at the respective first and second ends of the subscriber loop and report the values obtained. In this way a wanted signal can be decoupled from the subscriber loop.
In accordance with a further feature of the invention, the first and second circuits each supply a control signal for controlling the current at the first end and at the second end of the subscriber loop. This signal can be used to control a circuit for limiting overcurrent.
In accordance with an added feature of the invention, the first and second circuits respectively supply a first and a second input signal which correspond to the received signal from the subscriber line, and respectively receive a first and a second output signal which correspond to the transmitted signal in the subscriber line. In this way both the first and the second circuits provide a two-wire to four-wire conversion of the signals. The first and the second input signals and the first and the second output signals thus correspond to the wanted signals on the subscriber loop in the receiving direction, i.e. from the subscriber loop to the circuit configuration, and in the transmitting direction, i.e. from the circuit configuration to the subscriber loop.
In accordance with an additional feature of the invention, the first and second input signals and the first and second output signals are digital signals.
In accordance with yet another feature of the invention, the signals are generated through appropriate analog/digital converters and digital/analog converters in the first and second circuits. The use of digital signals has the advantage that they are easier to regenerate and thus the effect of interference can be minimized.
In accordance with yet a further feature of the invention, the first circuit and the second circuit are laid out identically. This has the advantage that it is only necessary to construct a single circuit which is then suitable for both the first and the second circuits. Similar advantages arise in the fabrication and in the use of the first and the second circuits in a circuit configuration according to the invention.
In accordance with yet an added feature of the invention, there is provided a third circuit which is connected with the first circuit and the second circuit in a dc decoupled way. In this configuration the third circuit provides the output signals and processes the arriving input signals. The dc decoupling has the advantage of permitting the third circuit to be operated at voltage levels which are independent of the voltage levels of the first and second circuits.
In accordance with yet an additional feature of the invention, the dc decoupled connection between the first circuit and the third circuit and between the second circuit and the third circuit is implemented through capacitors. Compared with the alternative of a transformer, capacitors used as dc decoupling elements have the advantage of being cheaper to fabricate with relatively high precision and having a smaller size in the necessary dimensioning range.
In accordance with again another feature of the invention, the third circuit has a control device which controls the first, second and third circuits.
In accordance with again a further feature of the invention, the first and second circuits are controlled through time-division multiplexing of a control signal in the first and second output signals.
In accordance with again an added feature of the invention, the third circuit has an echo compensator.
In accordance with again an additional feature of the invention, the third circuit has a coding circuit for coding the output signals.
In accordance with still another feature of the invention, the control device of the third circuit performs operating point control of the circuit elements in order to achieve a linear transmitted signal on the subscriber loop in the event of changing current consumption.
With the objects of the invention in view the circuit configuration of the invention is especially suitable for telephone subscriber loops of the ISDN (integrated services digital network). It is particularly suitable for the line codes 2B1Q, 4B3D and Up0. The circuit configuration is similarly suitable for an ISDN S-interface. Finally, the circuit configuration can be used to particular advantage for the connection of a telephone subscriber loop in the case of ADSL (asynchronous digital subscriber line), MDSL (multirate digital subscriber line), HDSL (high bit rate digital subscriber line), SDSL (single pair or symmetric digital subscriber line) and VDSL (very high bit rate digital subscriber line).
With the objects of the invention in view there is also provided a chip set for supplying a telephone subscriber loop having first and second lines with a supply voltage, for transmitting a transmitted signal into the telephone subscriber loop and for receiving a received signal from the telephone subscriber loop, the chip set comprising a first chip to be connected to the first line, the first chip supplying a first input signal and receiving a first output signal of the first line; and a second chip to be connected to the second line, the second chip supplying a second input signal and receiving a second output signal from the second line; the first and second chips being identical and requiring a supply voltage substantially lower than the power supply voltage supplied to the telephone subscriber loop. A chip set of this kind enables low-cost provision of a line termination for a telephone subscriber loop.
In accordance with another feature of the invention, a third chip receives the first and the second input signals and supplies the first and the second output signals.
It is advantageous for the input and output signals to be pre-processed in the third chip. For this purpose, in accordance with a further feature of the invention, the third chip has an echo compensator which deletes the echo of the transmitter on the subscriber loop.
In accordance with a concomitant feature of the invention, the third chip has an input/output device for a PCM bus.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit configuration and a chip set for supplying a telephone subscriber loop with a supply voltage and a network-side terminal of a telephone subscriber loop, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.